Design and Control of a Zero Voltage Switching MEMS DC-DC Power Converter

In this paper, we present the modelling, the design, and the control of a DC-DC voltage converter using a MEMS variable capacitor. We estimate, for a 12V-10V step-down converter, an efficiency of 88% and a power density of about 1.3mW/cm2. This converter is useful in low power portable applications, where several efficient DC-DC converters are necessary to convert the battery voltage into the voltages required by the loads. It can be used as well to convert the output voltage of an energy scavenger to a useful voltage. Its advantage is that it can be completely integrated on silicon as it does not contain an inductor element as in conventional buck and boost converters. Previous research work about MEMS converters is not sufficiently developed; two modes of variable capacitor operation have been explored: bistable static mode and resonant mode. Both methods have focused on obtaining high voltages for specific applications while efficiencies were very low. Our new conversion approach presents zero voltage switching; therefore the efficiency is high as the switching losses are close to naught.